Scientists say coral reefs around the world are experiencing mass bleaching in warming oceans

Reef scientists say coral reefs around the world are experiencing global bleaching for the fourth time due to prolonged warming of the oceans. Scientists from the National Oceanic and Atmospheric Administration and the International Coral Reef Initiative say bleaching has been documented across at least 53 countries over the past year. Bleaching happens when stressed coral expel the algae that are their food source and also give them their color. If the bleaching is severe and long-lasting, the coral can die. That matters because coral reefs are important ecosystems that sustain underwater life, protect biodiversity and slow erosion. They also support local economies through tourism.